Statement of the Technical Field
This document relates to co-channel spatial separation and non-coherent detection of communication signals. More particularly, this document concerns co-channel spatial separation and non-coherent detection of communication signals using matched Doppler filtering and non-coherent demodulation and equalization techniques.
Description of the Related Art
Automatic Identification Systems (“AISs”) are well known in the art. The AISs typically allow vessels (e.g., ships) to view and track marine traffic in a surrounding area. AISs have many applications. For example, AISs can be employed for collision avoidance, fishing fleet monitoring and control, vessel traffic services, maritime security, navigation services, search and rescue, accident investigation, and fleet and cargo tracking.
In this regard, an AIS is an automatic tracking system used on ships and by Vessel Traffic Services (“VTSs”) for identifying and locating vessels in a given geographic area or around the globe. A vessel's identification and location are tracked by exchanging data with other nearby vessels, AIS base stations and satellites. The vessel's identification and location are displayed in an AIS chartplotter or other Graphical User Interface (“GUI”) viewable on a display screen. The AIS chartplotter and other GUIs facilitate collision avoidance amongst a plurality of vessels in proximity to each other. Other information may also be displayed on the display screen, such as a vessel's position, course and/or speed.
The vessels comprise AIS transceivers which automatically and periodically transit vessel information. The vessel information includes, but is not limited to, vessel name, position, speed and navigational status. The vessel information can be used to track the vessel by the AIS base stations and/or satellites. The AIS transceivers comprise a Very High Frequency (“VHF”) transceiver and a positioning system (e.g., a Global Positioning System (“GPS”)). The VHF transceiver has a VHF range of about 10-20 nautical miles. The VHF transceiver operates in accordance with a Time Division Multiple Access (“TDMA”) scheme. The AIS base stations and satellites comprise AIS receivers, and therefore can receive AIS data but are unable to transmit their own locations to the vessels. The AIS receivers also operate in accordance with the TDMA scheme.
Recently, global AIS data has been made available on the internet. The global AIS data comprises data collected from satellites and internet-connected shore-based stations. The global data include vessel names, details, locations, speeds, and headings. The global data is displayed on a publically accessible map showing the relative locations of vessels around the globe.